The present invention relates to F-type connectors used in CATV applications, and more specifically to structure providing improved engagement of the RFI seal of such connectors against the connector face.
The frequencies of RF signals transmitted through coaxial cables to a subscriber TV set are typically in the range of 5 to 40 MHz. This frequency range is plagued with noise ingress that degrades system performance. Studies have shown that the majority of ingress is related to poorly installed F connectors. These connectors are normally mounted upon the end of a coaxial cable for connection to a port on the television set. Connection is usually made by the subscriber in the home via an internally threaded nut of the connector and an externally threaded stub shaft surrounding the port. For fully threaded connection, ensuring the necessary abutment of the RFI seal of the cable against the equipment connector face, the nut must be rotated up to 5 or 6 full revolutions. The typical, non-technical subscriber making the installation often fails to fully tighten the connector for one or both of two reasons: first, the visual performance functions may be obtained with a partial connection and, once the subscriber sees the video operating on the TV screen, it is assumed that the connection is satisfactory, and, secondly, the location of the equipment is often such that the subscriber must reach around and behind the equipment and thus cannot sec the port as the connector is being installed.
It is a principal object of the present invention to provide an F-type connector for threaded engagement with a port on a TV set or other equipment receiving RF signals through a coaxial cable to which the connector is mounted wherein a secure RFI seal is obtained in a simplified manner.
Another object is to provide an F-type connector having novel and improved features ensuring shielded connection to an input port and which is compatible with an end portion of a coaxial cable which has been prepared in an industry standard manner.
A further object is to provide an F-type connector with enhanced ease of proper installation which is compatible with either compression or crimp attachment of the connector to the coaxial cable.
Other objects will in part be obvious and will in part appear hereinafter.
The connector of the invention is disclosed in two embodiments each having a total of five elements, namely, a body, a nut, a post, a compression ring and a coil spring. The body, nut, post and compression ring are basically the same in structure and function as corresponding elements in conventional F connectors, and are mounted in similar manner upon the end of the coaxial cable. That is, the nut is connected to the flanged end of the post and is freely rotatable, although axially moveable, with respect thereto. The end of the cable is prepared for mounting to the connector by stripping away all covering layers from the central, rigid conductor for a first length, and stripping the braided, shielding layer and outer layer of dielectric material for a second length. The non-flanged end of the post is then forced between the aluminum conducting layer which surrounds the inner layer of dielectric material and the braided layer until the end of the inner dielectric layer and surrounding conducting layer are substantially coplanar with the surrounding, annular surface of the post. The relative axial positions of the nut and post are such that, in the typical case, six or seven full revolutions of the nut are required to bring the annular post surface into contact with the end of the stub shaft surrounding the port on the equipment to which the connector is attached; anything less than full contact of the connector post with the stub shaft, as previously mentioned, provides incomplete shielding and permits noise ingress.
In the connector of the present invention, the additional element, i.e., the coil spring, has opposite ends bearing against the underside of the post flange and a portion of the nut. The nut is axially movable to a limited degree with respect to the post (and other elements of the connector) between a first, or rest position, in which it is held by the spring prior to threading the nut onto the shaft, and a second position, wherein the nut is axially displaced by a maximum distance from the rest position. In the rest position, the threaded portion of the nut extends a short way, e.g., one or two thread revolutions, beyond the end of the inner dielectric layer and aluminum conducting layer of the coax cable and the surrounding, annular surface of the post. Thus, when the end of the nut is brought into contact with the end of the shaft, only one or two revolutions of the nut are required to establish contact of the post surface and shaft, thereby providing an acceptable degree of shielding to prevent ingress of noise and degradation of signal at the connector-equipment interface. However, the connector of the invention permits further threaded engagement of the nut and shaft by compression of the spring upon continued rotation of the nut as the latter moves axially with respect to the post.
In the first disclosed embodiment, the elements are assembled by inserting the non-flanged end of the post into the connector body until the latter abuts the underside of the flange, then placing the spring in surrounding relation to the body with one end contacting the underside of the flange, outwardly of the body. The nut is then placed over the post flange and spring with the inner end of the threaded portion of the nut contacting the post flange on the surface opposite a first end of the spring and the other, open end of the nut extending past the other end of the spring. This open end of the nut is then deformed, i.e., peened over, to a diameter less than that of the spring, whereby the ends of the spring are captured between the underside of the post flange and the deformed end of the nut. Axial movement of the nut relative to the post in a direction moving the threaded end of the nut away from the post, as when the nut is threaded onto the shaft of the equipment input port, thus compresses the spring. Conversely, when the threaded connection is removed, the spring moves the nut back to its aforementioned rest position with respect to the post.
In the second disclosed embodiment, the spring is captured between the underside of the post flange and an integrally formed flange on the inside of the nut, spaced from the threaded portion thereof. In this case, the spring surrounds the post (rather than the body), the elements being assembled by placing the spring within the nut, one end of the spring contacting the ingral flange within the nut, then inserting the post through the nut and mounting the body upon the post below the nut. This embodiment has the advantage that no deforming or peening operation is required in assembly of the elements; however, a non-standard preparation of the end of the coax cable is required due to the spacing of the end of the body from the underside of the post flange.